The invention relates generally to the field of electronic photography, and in particular to techniques for mounting a sensor to an optical assembly.
An important attribute of a digital camera is for the surface of a sensor, e.g., a charge coupled device (CCD), to be perpendicular to the optical centerline of the lens used to image a subject upon the sensor. The degree of tilt between the CCD and the optical centerline directly affects the image quality of the system. Therefore, care should be given to reduce or eliminate this tilt. For high cost/low volume cameras, the CCD is xe2x80x9cactively alignedxe2x80x9d to the lens. This means that each individual camera is adjusted to eliminate this tilt. Currently, this is a very expensive and time-consuming process which is impractical when manufacturing low cost/high volume cameras. Consequently, most lower cost digital cameras do not actively align the CCD. Instead, they typically mount the CCD to a very flat plate (with screws) and then mount the plate to the lens assembly. By controlling the flatness of the plate and CCD package, and the perpendicularity of the lens mount to the optical centerline, the resulting tilt can often be controlled to an acceptable degree. However, not only does the CCD plate adds cost and assembly time, but it still results in greater variation of lens/CCD tilt than can be tolerated in certain applications.
JP 1-133012 (Fujino) describes a sensor assembly in which tapered pins are used to facilitate positioning of an image sensor relative to an optical assembly. In particular, two spring-loaded tapered pins are set into the optical assembly through two openings in the lead frame of the image sensor to establish the position of the image sensor relative to the optical axis of the optical assembly. A number of problems are evident in this sensor assembly. The tapered pins are set into machined holes in the optical assembly, which allows (due to tolerances) for some variation in the position of the sensor. More importantly, the taper of the two pins does not provide adequate control of the tilt of the sensor assembly relative to the optical axis.
The problem is to provide a simple assembly system that minimizes tolerances while rigorously controlling the tilt as well as the x-y position of the sensor relative to the center line of the optics.
This invention departs from the prior art by controlling tilt without having to depend upon the flatness of a plate or the tolerance of holes through the lead frame of the sensor assembly. The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a sensor package assembly for use with an optical assembly includes an optics base mechanism for supporting the optics assembly in relation to an optical axis, an image sensor mounted on a lead frame, and a sensor mounting frame for locating and supporting the image sensor in relation to the optical axis. The optics base mechanism has at least three optics-related locator features, and the sensor mounting frame also has at least three frame-related locator features. By fastening the optics base mechanism and the sensor mounting frame together such that the optics-related locator features are oriented in opposed relation to the frame-related locator features with the lead frame pinched therebetween, the tilt of the image sensor is controlled relative to the optical axis.
This invention uses the surface of the lead frame (which is the sheet metal that the CCD imager is attached to) of the CCD sensor assembly to control the lens/CCD tilt. According to the preferred embodiment, the lead frame of the sensor assembly is pinched between a sensor mounting frame and an optics base mechanism in three places so that the CCD lead frame is directly located to the optics base mechanism. By eliminating the CCD plate (and not locating to the plastic part of the CCD sensor) the tolerances that affect the lens/CCD tilt are reduced. Also, the invention provides a xe2x80x9cz-axisxe2x80x9d assembly (all parts are assembled in the same direction), which is desirable Bower assembly time/cost) in a high volume manufacturing environment. In contrast, the assembly procedure when using a CCD plate ordinarily does not maintain a xe2x80x9cZ-axisxe2x80x9d approach, since the screws that attach the plate to the optics base mechanism would typically be driven in a direction opposite to the remainder of the assembly.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.